N-type ZnTe layers with high electron concentration are grown by molecular-beam epitaxy using aluminum as the donor species. The ZnTe:Al layers show a high structural quality with a narrow x-ray diffraction linewidth (24 arcsec) and a high carrier concentration up to n=4×1018 cm−3 with low resistivity (ρ=0.017 Ω cm). The dependence of the electron mobility on the carrier concentration suggests that the dominant scattering mechanisms in the ZnTe:Al layers are ionized impurity scattering and polar optical phonon scattering. The photoluminescence spectrum of moderately doped ZnTe layers shows strong Al–donor-related bound exciton lines: I2 (2.378 eV) and donor–acceptor pair emission (zero phonon energy=2.324 eV) with a weak deep-level emission (2.19 eV). Highly Al-doped layers show an increase in the deep-level emission intensity and a decrease in carrier mobility, which are interpreted in terms of the increase in the carrier compensation.

A ZnCdTe/ZnTe/ZnMgSeTe quantum-well (QW) structure lattice matched to ZnTe is proposed for the light-emitting devices in the pure-green wavelength region. Thin ZnTe layers are inserted in between the ZnCdTe QW layer and ZnMgSeTe cladding layers, which improve the quality of the QW structure as demonstrated by its narrow photoluminescence line width (6.5 meV at 10 K). Optically pumped lasing at 552 nm at room temperature with a threshold optical power of 215 kW cm−2 is achieved. The present results clearly show the feasibility of ZnTe-based QW structures for the application to light-emitting devices in the pure-green wavelength region.

We have investigated the ZnTe-based material system for the application to light-emitting devices. To this end, ZnTe homoepitaxy techniques have been developed to grow high-quality epitaxial layers. The conductivity control of ZnTe and ZnMgSeTe layers have been investigated. High structural quality n-type ZnTe layers with high carrier concentration are achieved by aluminum doping. Ambipolar conductivity control of quaternary layers is achieved. Aluminum doped ZnMgSeTe layers show a net carrier concentration of 5 Â 10 16 cm À3 , while a high hole concentration of 2.5 Â 10 19 cm À3 is achieved by p-type doping using a nitrogen plasma source. Based on those results, Zn 1Àx Cd x Te/ZnMgSeTe triple-quantum-well(TQW) LED structures were fabricated. Bright electroluminescence was obtained at room temperature at the wavelength of 604 nm from Zn 0:7 Cd 0:3 Te and at 566 nm from Zn 0:85 Cd 0:15 Te TQW-LED.Introduction Devices emitting light at around 550 nm are strongly needed for several important applications such as medical, plastic optical fiber communication, and full color laser display applications. Although laser diodes (LDs) for violet to blue-green and red wavelength ranges are now commercially available, no succesful report on LDs in the wavelength range from the pure-green to yellow (l = 540-580 nm) have been reported yet. Moreover, the conversion efficiency of light-emitting diodes (LEDs) in this wavelength region is extremely low in comparison with that of blue and red LEDs [1].ZnTe has a direct band gap of 2.27 eV (546 nm) at room temperature, therefore it is one of the most important materials for the pure-green wavelength (l = 550 nm) region. Because of the importance of ZnTe, there have been continuous attempts to fabricate ZnTe-based LEDs. Homo-junction LEDs were fabricated by diffusion of donor impurities [2,3]. However, ZnTe-based heterojunction LEDs have not been demonstrated yet, mainly due to the problems in growing highly doped n-type epitaxial layers with high crystal quality.In this paper, molecular beam epitaxy of ZnTe-based high-quality thin films by homoepitaxy technique is reported. The conductivity control of ZnTe-based materials is investigated using aluminum and nitrogen plasma sources as a n-and p-type dopants. Heterojunction LED strutures are fabricated and current injected operation at room temperature is demonstrated.

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